why is this llvm IR generated by my compiler is segfaulting
I'm building a compiler for university project And I'm using llvm.
I have generated this IR for a minimal program :
; ModuleID = 'Main'
source_filename = "Main.java"
%A = type { i16 }
%Main = type { i16 }
@progvtable = constant [1 x <{ i16, i8*, i8* }>] [<{ i16, i8*, i8* }> <{ i16 0, i8* getelementptr inbounds ([5 x i8], [5 x i8]* @1, i64 0, i64 0), i8* bitcast (i64 (%A*)* @getX to i8*) }>], align 8
@0 = constant [8 x i8] c"%lld %c 0", align 8
@1 = constant [5 x i8] c"getX 0", align 8
declare i32 @strcmp(i8*, i8*)
define i8* @vlookup(i16 %type, i8* %funcname) {
vlookup:
%i = alloca i64, align 8
%finalres = alloca i8*, align 8
store i64 0, i64* %i, align 8
store i8* null, i8** %finalres, align 8
br i1 true, label %loop, label %endloop
loop: ; preds = %loop, %vlookup
%0 = load i64, i64* %i, align 8
%1 = getelementptr inbounds [1 x <{ i16, i8*, i8* }>], [1 x <{ i16, i8*, i8* }>]* @progvtable, i64 0, i64 %0
%2 = getelementptr <{ i16, i8*, i8* }>, <{ i16, i8*, i8* }>* %1, i32 0, i32 0
%3 = load i16, i16* %2, align 8
%4 = getelementptr <{ i16, i8*, i8* }>, <{ i16, i8*, i8* }>* %1, i32 0, i32 1
%5 = load i8*, i8** %4, align 8
%6 = getelementptr <{ i16, i8*, i8* }>, <{ i16, i8*, i8* }>* %1, i32 0, i32 2
%7 = load i8*, i8** %6, align 8
store i8* %7, i8** %finalres, align 8
%8 = icmp eq i16 %3, %type
%9 = call i32 @strcmp(i8* %5, i8* %funcname)
%10 = icmp eq i32 %9, 0
%11 = and i1 %10, %8
%12 = add i64 %0, 1
store i64 %12, i64* %i, align 8
br i1 %11, label %loop, label %endloop
endloop: ; preds = %loop, %vlookup
%13 = load i8*, i8** %finalres, align 8
ret i8* %13
}
declare i32 @printf(i8*, ...)
declare i8* @GC_malloc(i64)
define %A* @A_init() {
A_init:
%0 = call i8* @GC_malloc(i64 2)
%this = bitcast i8* %0 to %A*
%1 = getelementptr inbounds %A, %A* %this, i32 0, i32 0
store i16 0, i16* %1, align 8
ret %A* %this
}
define i64 @getX(%A* %this) {
getX:
ret i64 1
}
define %Main* @Main_init() {
Main_init:
%0 = call i8* @GC_malloc(i64 2)
%this = bitcast i8* %0 to %Main*
%1 = getelementptr inbounds %Main, %Main* %this, i32 0, i32 0
store i16 5, i16* %1, align 8
ret %Main* %this
}
define void @main(i8**) {
main:
%1 = alloca i8**, align 8
store i8** %0, i8*** %1, align 8
%args = load i8**, i8*** %1, align 8
%2 = alloca %A*, align 8
%3 = call %A* @A_init()
store %A* %3, %A** %2, align 8
%e = load %A*, %A** %2, align 8
%4 = getelementptr inbounds %A, %A* %e, i32 0, i32 0
%5 = load i16, i16* %4, align 8
%6 = call i8* @vlookup(i16 %5, i8* getelementptr inbounds ([5 x i8], [5 x i8]* @1, i64 0, i64 0))
%7 = bitcast i8* %6 to i64 (%A*)*
%8 = call i64 %7(%A* %e)
%9 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([8 x i8], [8 x i8]* @0, i64 0, i64 0), i64 %8, i8 10)
ret void
}
Currently this is unoptimized output but that's not the problem, I llc the above ,I then use gcc to link libgc.so and then I run the application and it segfaults.
Using gdb I verified that segfaults happen on the call to strcmp , lldb showed that one of either parameters is null.
I look thoroughly at the IR and I don't see any issue with it, yet it segfaults , why is this happening ?
For the record @progvtable is my representation of virtual tables to support polymorphism in the language I'm going to implement.
I'm using llvm 4 and gcc 7.1.1 , my OS is Arch Linux x64.
Silly me, The problem is very trivial xD it's here :
br i1 %11, label %loop, label %endloop
The problem with this instruction is that the condition operand is to break the loop not continue it , all what was required is to switch label %loop and label %endloop places.